1. Field of the invention
The present invention concerns a material directly usable as a heat protection or dissipation shield.
This material is of particular benefit by virtue of the phenomenon of hydration and superheating that occurs within it during thermal attack.
2. Description of the prior art
Various known devices and methods for implementing heat protection or dissipation shields based on this phenomenon are designed to protect objects which have to resist for relatively long periods thermal attack that can be extremely intense (such as a fire or other thermal phenomenon corresponding to temperatures that can exceed 2,000.degree. C.).
There has already been proposed a heat dissipation shield comprising between two walls respectively called the hot wall and the cold wall a layered hydrating element in contact with the cold wall, a layered superheating element between the hydrating element and the hot wall, and a layered porous refractory element between the superheating element and the hot wall, and the latter being formed with orifices to enable the saturated steam developed within the hydrating element when the shield is functioning and superheated during its passage through the superheating element to escape to the exterior of the hot wall (French patent No. 69.05203).
With a heatshield of this kind it is possible to provide effective thermal protection for temperatures not exceeding the temperature at which the liquid contained in the hydrating agent vapourizes throughout the period of vapourization without any increase in pressure (for example: 100.degree. C. in the case of water at the standard atmospheric pressure of one bar) throughout a time period directly proportional to the quantity of this liquid contained in the hydrating element.
As is hardly surprising, a heatshield of this type can only be used under specific circumstances and in specific quantities.
There is also known a heatshield consisting primarily of a flexible material in the form of an array or mat of fibers serving as a support or armature for a powder material capable of absorbing and retaining a liquid to yield a paste or gel that is highly thixotropic, this hydrating/superheating element evolving in the presence of the liquid from the hydrating function towards the superheating function as the thermal attack proceeds. The manufacture of a heatshield of this kind entails disposing the hydrating/superheating element between two flexible coating elements, one intended to be in intimate contact with the surface of the object to be protected and the other constituting the outside surface of the heatshield (U.S. Pat. No. 4,482,111), these two coating elements serving also as sealing skins providing resistance to aging in a normal environment.
The manufacture of a heatshield of this kind therefore has to take account of this aging phenomenon and consequently the sealing material makes an important contribution to the effectiveness of the finished product.
Finally, there has already been proposed a thermal protection or dissipation shield offering a more extended range of protection or stabilization temperatures for the object to be protected and significantly increasing the duration of such protection, temperature stabilization being effected at different and decreasing levels from the hot surface (the area exposed to thermal attack) towards the cold surface delimiting the area to be protected.
A screen of this kind comprises a composite assembly also including a hot wall and a cold wall and between these two walls at least two adjacent vaporizing/superheating elements in a flexible, rigid or stiffened material each containing within it a substance capable of releasing at a temperature specific to each element a non-inflammable gas or vapor, each element being separated from the other by a flexible or rigid wall that is sealed at the temperature at which steam or gas is released from the element nearest the hot wall but adapted to become porous immediately this temperature is exceeded, this element--because of the presence of said substance--evolving from the "vaporizing" function towards the "superheating" function as the thermal attack to which it is subjected proceeds (U.S. Pat. No. 4,592,950).
In this latter type of shield it is equally necessary to use sealing skins. This constraint may be prejudicial in numerous applications.
The present invention therefore proposes a material directly usable as a thermal protection or dissipation shield without any other modification than forming to shape and with no additional conditions as to packaging or storage concerning sealing.